Manufacture of alkali perborates



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OTTO LIEBKNECHT, OF FRANKFORT-ON-THE-MAIN, GERMANY, ASSIGNOR, To THE ROESSLER & HASSLACHEB, CHEMICAL COMPANY, OF NEW YORK, N. Y., A. 003- PORATION OF NEW YORK.

MANUFACTURE OF ALKALI PERBORATES.

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T 0 all whom it may concern:

Be it known that I, OT'roLIEBKNEoH'r, a subject of the German Emperor, and resident of Frankfort-on-the-Main, Germany, have invented certain new and useful Improvements in the Manufacture of Alkali Perborates, of which the following is a specification.

My invention relates to the manufacture of alkali perborates such as, forinstance, sodium perborate, and in particular to the electrolytic manufacture of alkali perborates from lyes containing soda and borax. It is the object of my present invention to provide improvements in the electrolytlc manufacture of alkali perborates from lyes containing soda and borax, the said improvements resulting in a purer and more stable perborate, and incidentally, 1n a more economical operation.

In electrolytically producing alkali perborates from lyes containing soda and borax, it has been found that the proportion of bicarbonate in the electrolyte gradually increases so that finally the bicarbonate is precipitated synchronously with the perborate and dilutes the latter. The bicarbonate thus precipitated not only produces an undesirable dilution of the perborate, but it has been found that the same involves the further drawback of exercising an unfavorable influence on the stability of the perborate. According to the inventors investigations, the undesired formation of the bicarbonate appears to be due to the fact that the carbonic! acid released during the process combines to its greater part with the soda contained in the solution; a phenomenon being somewhat surprising as generally carbO(I11lC acid does not readily combine with so a.

On account of this knowledge care is to be taken in producing alkali-perborate electrolytically to avoid an excessive rise in the proportion of bicarbonate in the lye. This can be attained for instance, by entirely, or

' partly, replacing the addition of soda and borax, required to supply the alkali and boric acid consumed as rate, by metaborate or y free alkali and borax. In such a manner an undesired strong formation of bicarbonate, already Specification of Letters Patent.

recipitated perbo- Patented N 0V. 1, 1921.

Application .filed January 27, 1917. Serial No. 145,018.

during the electrolysis can be prevented and the proportlon in the lye be kept favorable for the electrolytic process.

In the electrolyzing of solutions saturated with soda and borax, synchronous precipitation of bicarbonate does not take place unless the proportion of bicarbonate in the ialtectrolyte exceeds about 70 to 75 grams per An example may illustrate the process.

A solution saturated with soda and borax was electrolyzed. On completion of the first stage of the operation the electrolyte contained 42 grams of bicarbonate per liter. After removal of the perborate the lye saturated with soda and borax became subjected to a second treatment oncompletion of which the proportion of bicarbonate had risen to 74 grams per liter electrolyte.

In order to prevent a further increase of the proportion of bicarbonate, from 16 to 18 grams of sodium hydrate were added to each liter of the electrolyte prior to reach further treatment; the result of this additlon of sodium hydrate was that the proportion of bicarbonate averaged 60 grams per liter of the electrolyte on completion of each operation. The perborate produced was practically free of bicarbonate, and .Very stable. 1

Instead of combining with an alkali the carbonic acid produced during the opera tion, an alternative method consists in removing the carbonic acid from the waste lye prior to its repeated utilization. For instance in combining the carbonic acid present as bicarbonate with lime in order to convert the bicarbonate into soda, I have found that it is not advantageous to carry this caustification to an extent to produce free alkali although the free alkali is used for the formation of metaborate by the coaction of borax and is again converted into soda by the carbonic acid forming during the electrolytic action. Instead of lime, other earth-alkali hydrates or oxids or free alkali could likewise be use for neutralization.

This alternative method will be explained by another example.

A waste lye having twice been used as an electrolyte and containing thereafter 72 

